CN104874365A - Carboxymethyl cellulose ion intercalated hydrotalcite-like composite material, and preparation method and application thereof - Google Patents

Abstract

The invention discloses a carboxymethyl cellulose ion intercalation hydrotalcite composite material and its preparation method and application. The general chemical formula of the composite material is [M ²⁺ _1-x M ³⁺ _x (OH) ₂ ] ^x+ (A ^- ) _x ·mH ₂ O, where M ²⁺ is Zn ²⁺ , Ca ²⁺ or Mg ²⁺ , M ³⁺ is Fe ³⁺ or Al ³⁺ , M ²⁺ and M ³⁺ are located in the main layer of hydrotalcite Above; A ^2- is the interlayer carboxymethyl cellulose anion; x is the molar ratio of M ³⁺ /(M ²⁺ +M ³⁺ ), 0.1≤x≤0.33; m is the number of interlayer water molecules, m=3-6. The hydrotalcite-like composite material of the present invention adopts the calcining intercalation method, and the carboxymethyl cellulose anion rich in o-hydroxyl groups is intercalated and assembled between the hydrotalcite-like layers to prepare the hydrotalcite-like composite material with a typical lamellar structure As an adsorbent, it is applied to the selective adsorption and removal of borate anions in water. It can be used as a new type of environmental material for the separation and adsorption of boron in wastewater and seawater desalination. The product has high thermal stability and mechanical stability, is environmentally friendly, has a simple preparation process, and is easy to realize industrialization.

Description

Carboxymethyl cellulose ion intercalation hydrotalcite composite material and its preparation method and application

technical field

The invention belongs to the technical field of preparation of inorganic-organic composite functional materials, and in particular relates to a carboxymethyl cellulose ion intercalation hydrotalcite-like composite material and its preparation method and application .

Background technique

With the development of economy and society, the current environmental pollution has become a major challenge faced by human beings. The pollution of various water bodies has continued to intensify, resulting in the continuous deterioration of the ecological environment and seriously affecting people's health and quality of life. Among them, boron, as an important chemical raw material, is widely used in practice, but the boron pollution caused by the discharge of boron-containing wastewater needs to be solved urgently. At present, the adsorbents that can be used to separate and remove boron in solution can be mainly divided into three types: inorganic adsorbents, organic polymer adsorbents and organic/inorganic hybrid boron adsorbents. Inorganic boron adsorbent has firm structure, good thermal stability and low preparation cost, but has low adsorption capacity for boron and no special selectivity, and is easily affected by coexisting ions. Organic adsorbents with N-methylglucosamine as the adsorption functional group have specific effects and high adsorption capacity for boron, but due to their structural particularity and water insolubility, they show mechanical properties and poor adsorption capacity in practical applications. Defects such as poor hydrophilicity seriously affect its performance. Now it is urgent to find one or a class of adsorbents with high stability, high selectivity, low cost and high efficiency to realize the efficient removal of boron, which is a hot and difficult point in the current research on boron removal by adsorption. Composite is the development trend of modern materials, and the performance complementation and optimization can be achieved through the compounding of various material functions, among which organic/inorganic hybrid materials are the most dazzling new stars in the composite material family. Scholars at home and abroad have attempted to prepare organic/inorganic hybrid boron adsorbents by loading or grafting ortho-hydroxyl compounds on mesoporous materials or silica gel.

Cellulose is the oldest and most abundant natural polymer on the earth, and it is the most precious natural renewable resource that is inexhaustible and inexhaustible. Carboxymethyl cellulose (CMC) is based on natural cellulose and is the most widely used and most used type of cellulose in the world today. It is an electrolytic polymer produced by alkalization and etherification with low cost. Because carboxymethyl cellulose contains many hydrophilic hydroxyl groups and carbonyl groups, it has certain adsorption properties for metal ions and dyes. However, its ability to adsorb ions is not strong, and it must be chemically modified to have more or stronger hydrophilic groups in order to reduce costs and improve performance, making it a good adsorption material.

Hydrotalcite-like (LDHs), as a class of double metal hydroxides with a layered structure, has attracted extensive research attention due to its adjustable composition, high surface adsorption performance and unique thermal stability. focus on. When the interlayer ions of LDHs are inorganic ions such as CO ₃ ^2- , NO ₃ ^- and Cl ^- , hydrotalcite can be used to adsorb boron in solution, but the adsorption capacity is not high. Between the hydrotalcite-like layers, organic acids such as tartaric acid, citric acid, and malic acid are inserted to adsorb metal ions in water. It has been reported that the introduction of organic matter into the interlayers of hydrotalcites can prepare many functional materials with special properties compared with their precursors.

The new organic/inorganic hybrid boron adsorbent prepared by intercalating carboxymethylcellulose ions rich in o-hydroxyl groups between the hydrotalcite-like layers will achieve very meaningful results. On the one hand, due to the introduction of carboxymethyl cellulose between the hydrotalcite-like layers, it can not only selectively adsorb boron as the adsorption active center, but also improve the interface polarity and chemical microenvironment of the material, increase the interlayer distance, and reduce the surface area. energy, the adsorption capacity can be significantly enhanced; on the other hand, due to the introduction of the hydrotalcite-like inorganic material matrix, the adsorption material can have high mechanical and thermal stability, and is conducive to regeneration and recycling. In addition, hydrotalcite-like and carboxymethyl cellulose are widely sourced, low-cost, and good environmental compatibility, so that this type of adsorbent will have broad application prospects. However, there are no reports on the preparation of hydrotalcites intercalated with carboxymethylcellulose anions and their adsorption of boron.

Contents of the invention

The object of the present invention is to provide a low-cost, easy-to-manufacture carboxymethyl cellulose intercalated hydrotalcite-like composite material, which is environmentally friendly, has high thermal stability and mechanical stability, and has a high adsorption capacity for boron at room temperature , can be used for the separation and removal of boron in water.

To achieve the above object, the technical solution adopted in the present invention is:

The hydrotalcite-like composite material of the present invention adopts the calcining intercalation method, and the carboxymethyl cellulose anion rich in o-hydroxyl groups is intercalated and assembled between the hydrotalcite-like layers to prepare the hydrotalcite-like composite material with a typical lamellar structure , the product has the characteristics of high thermal and mechanical stability, environmental friendliness, etc., and has a simple preparation process and is easy to realize industrialization. A large number of adjacent hydroxyl groups in the organic-inorganic composite material can chelate and adsorb boron, and can be used for the separation and adsorption of boron in waste water and seawater desalination. Compared with existing boron adsorbents such as boron-removing resins, this carboxymethylcellulose anion-intercalation hydrotalcite material not only has high mechanical strength, low preparation cost, and high boron adsorption capacity, but also has a significant effect on boron in the solution. The special effect adsorption effect of boron is expected to be applied in industry as a new type of boron special effect adsorption material.

The general chemical formula of a kind of carboxymethyl cellulose ion intercalation hydrotalcite composite material of the present invention is

[M ²⁺ _1-x M ³⁺ _x (OH) ₂ ] ^x+ (A ^- ) _x mH ₂ O, where M ²⁺ is Zn ²⁺ , Ca ²⁺ or Mg ²⁺ , M ³⁺ is Fe ^{3 +} or Al ³⁺ , M ²⁺ and M ³⁺ are located on the main layer of hydrotalcite; A ^2- is the interlayer carboxymethyl cellulose anion; x is M ³⁺ /(M ²⁺ +M ³⁺ ) Molar ratio, 0.1≤x≤0.33; m is the number of interlayer water molecules, m=3-6; the crystal structure of this material is that of a hydrotalcite-like material;

A kind of preparation method of carboxymethyl cellulose ion intercalation hydrotalcite composite material of the present invention, comprises the following steps:

1) Dissolve soluble divalent metal salts and trivalent metal salts in deionized water in a certain molar ratio, and stir to obtain solution A, in which the molar ratio of divalent and trivalent metal ions is (1~4): 1, divalent The metal ion concentration is 0.05~0.10 mol·L ^-1 ;

2) Under strong stirring, add sodium hydroxide solution drop by drop to solution A, adjust pH to 9~10 with sodium hydroxide solution, keep stirring at room temperature for 1~3h, filter and wash the resulting mixture several times to Neutral, the obtained filter cake is put into a constant temperature drying oven at 80~120℃ and dried for 4~6h to obtain a white solid B, which is the layered double metal hydroxide material LDH;

3) Put the solid B obtained above in a muffle furnace at 300-600°C for 3-5 hours to obtain a white solid powder C, which is a layered bimetallic composite oxide LDO;

4) Disperse the layered bimetallic composite oxide LDO prepared above in deionized water in a certain proportion to obtain suspension D;

5) Sodium carboxymethyl cellulose solid was dissolved in distilled water to obtain sodium carboxymethyl cellulose solution E;

6) Mix the LDO suspension D obtained in the above step 4) with a certain proportion of sodium carboxymethyl cellulose solution E, and stir mechanically for 6~10 hours to keep the solution in the flask alkaline at pH 8~10; mix the above mixture Transfer to a polytetrafluoroethylene hydrothermal crystallization kettle, crystallize in an oven at 80~150°C for 12~20h, cool to room temperature, separate the solid and liquid from the product, wash to neutral and then vacuum dry at 60~85°C for 2~10h , that is, a hydrotalcite-like composite material intercalated with carboxymethyl cellulose anions, which is denoted as LDH-CMC.

The divalent metal divalent metal salt is Zn ²⁺ , Ca ²⁺ or Mg ²⁺ nitrate, and the trivalent metal salt is Fe ³⁺ or Al ³⁺ nitrate.

The concentration of the sodium hydroxide is 0.50-4.0 mol·L ^-1 , and the stirring speed of the vigorous stirring is 300-450 rpm.

The molar ratio of the sodium carboxymethylcellulose to the trivalent salt is 1:1 to 3:1.

The mass ratio of the layered bimetallic composite oxide LDO to deionized water is 1% to 3%, the concentration of the sodium carboxymethylcellulose solution E is 1% to 3%, and the LDO suspension The volume ratio of turbid liquid D to sodium carboxymethyl cellulose solution E is 1:1~1:3.

Utilizing the chelating principle of boron by ortho-hydroxyl groups, the above-mentioned hydrotalcite-like composite material rich in ortho-hydroxyl groups intercalated with carboxymethyl cellulose anions was used as an adsorbent for the selection of borate anions in water Sexual adsorption removal.

Compared with the prior art, the present invention has the following advantages:

1) This technology adopts calcined intercalation method to synthesize LDH-CMC with controllable particle size and shape, which has special selective adsorption capacity for boron in solution, thus expanding the types of boron adsorbents; in addition, the material obtained by this method is overall Uniform, chemical composition and structure are microscopically adjustable;

2) Compared with ordinary LDH, LDH-CMC obtained by carboxymethylcellulose anion intercalation has more adjacent hydroxyl groups, which can further improve the selectivity and adsorption capacity of the product boron, and can adsorb efficiently in a short time Boron; Compared with ordinary CMC, LDH-CMC has the advantages of high mechanical strength and easy recycling;

3) The organic-inorganic composite material obtained by this technology has the characteristics of both inorganic and organic adsorbents. Compared with traditional boron adsorbents such as organic adsorbents such as boron-removing resins or inorganic adsorbents such as hydrated oxides, it has high mechanical strength, High adsorption capacity, special effect selectivity, low price and other advantages;

4) The technology is simple and easy to implement, has no pollution, and has strong practicability, and the obtained products have a wide range of applications.

Description of drawings

Fig. 1 is the X-ray diffraction (XRD) pattern of Mg-Al-LDH, Mg-Al-LDO and Mg-Al-CMC in Example 1.

FIG. 2 is a Fourier transform infrared (FTIR) diagram of Mg-Al-LDH, Mg-Al-LDO and Mg-Al-CMC in Example 1. FIG.

Fig. 3 is the thermogravimetric weight loss (TG-DSC) graph of Mg-Al-LDH and Mg-Al-CMC in Example 1.

Fig. 4 is a high-resolution field emission scanning electron microscope (HRSEM) image of Mg-Al-LDH, Mg-Al-LDO and Mg-Al-CMC in Example 1.

Fig. 5 is the adsorption effect diagram of Mg-Al-LDH, Mg-Al-LDO and Mg-Al-CMC to boron in embodiment 1.

Fig. 6 is a comparison diagram of the boron adsorption effect of Mg-Al-CMC in Example 1 and Mg-Al-CMC in Example 2.

Detailed ways

The technical solutions of the present invention will be further described below in conjunction with specific examples, but the protection scope of the present invention is not limited to these examples.

Example 1

(1) Synthesis of Mg-Al hydrotalcites with a molar ratio of 2: Dissolve 5.12g of magnesium nitrate and 3.75g of aluminum nitrate in 100mL

Distilled water is made into a mixed solution; then 4g of sodium hydroxide is dissolved in 100mL of distilled water to make a mixed alkali solution. The two solutions were dropped into a three-necked flask filled with 100 mL of distilled water under constant stirring at room temperature. After the dropwise addition, adjust the pH to 9-10 with 1mol·L ^-1 sodium hydroxide, and keep stirring at room temperature for 2h. The obtained mixture was suction-filtered and washed several times to neutrality, and the obtained solid was dried in a constant temperature drying oven at 80° C. for 4 hours to obtain Mg-Al double metal hydroxide Mg-Al-LDH.

(2) Place the Mg-Al-LDH solid in a muffle furnace at 450°C for 4 hours to obtain a white solid Mg-Al

Double metal oxide Mg-Al-LDO.

(3) Disperse the Mg-Al-LDO in 100mL distilled water with an ultrasonic cleaner to obtain a Mg-Al-LDO suspension.

(4) Weigh 4.5g sodium carboxymethylcellulose (CMC for short) and dissolve it in 100mL distilled water, then add it dropwise to

In the Mg-Al-LDO suspension, mechanically stir for 4 hours to keep the solution in the flask alkaline at pH 9-10; transfer the mixture to a polytetrafluoroethylene hydrothermal reaction kettle for crystallization in an oven at 80°C for 12 hours , filtered, washed to neutral, dried at 80°C, and ground to obtain a Mg-Al-CMC sample.

Fig. 1 is the X-ray diffraction (XRD) pattern of Mg-Al-LDH, Mg-Al-LDO and Mg-Al-CMC in Example 1. It can be seen from the figure that at 2θ=11.26°, 22.8°, 34.34°, 60.50°, and 61.64°, the obtained product Mg-Al-LDH all exhibits the characteristic diffraction peaks of hydrotalcite (003), (006) , (009), (110), and the diffraction peaks of the prepared samples are high and narrow, and there are few miscellaneous peaks, indicating that the prepared hydrotalcite-like is a single crystal phase with extremely high crystallinity. In the Mg-Al-LDO obtained by roasting the Mg-Al-LDH solid at 400 °C, the characteristic diffraction peaks of Mg-Al-LDH crystals completely disappeared, and the characteristic diffraction peaks of bimetallic composite oxides (LDO) appeared at the same time. In the Mg-Al-CMC obtained by intercalating CMC with Mg-Al-LDO, the characteristic peaks of Mg-Al-LDH crystals reappeared, and obviously shifted to a small angle, indicating that the layered structure of the hydrotalcite was restored, and the obtained composite The material has the same crystal structure as hydrotalcite-like.

Fig. 2 is the Fourier transform infrared spectrum (FTIR) diagram of Mg-Al-LDH, Mg-Al-LDO and Mg-Al-CMC in Example 1. In the figure, the relatively broad bands at 3400cm ^-1 are the -OH vibration bands of physically adsorbed water or crystal water and the stretching vibration bands of M-OH, and there are also weak bending vibration bands of water at 1630cm ^-1 . The MO vibrational band is at 780-890cm ^-1 . After CMC was intercalated into Mg-Al-LDH, the vibration peak of crystallization water near 1630 cm ^-1 basically returned to the level before calcination, and the symmetrical stretching vibration band of carboxylate -COO- appeared at 1380 cm ^-1 , ^and at 1040 cm -1 ¹ The CO stretching vibration peak appears. The FT-IR spectrum shows that CMC has entered the interlayer position of Mg-Al-LDO, realizing the intercalation assembly of the supramolecular structure of carboxymethylcellulose pillared hydrotalcite.

Fig. 3 is the thermogravimetric weight loss (TG-DSC) diagram of Mg-Al-LDH and Mg-Al-CMC. It can be seen from the figure that Mg-Al-LDH releases physically adsorbed water at about 110 ℃, the endothermic peak at about 230 ℃ is the removal of interlayer crystal water, and about 370 ℃ corresponds to the decomposition and combustion of interlayer organic species. Corresponding to the above process, there are three obvious weightless platforms in the TG curve. The TG diagram of Mg-Al-CMC reflects three weight loss stages, from room temperature to 240 ° C, the loss of surface adsorption water and interlayer water; 257 ~ 380 ° C is the removal of interlayer crystal water; around 440 ° C is the decomposition of interlayer CMC Combustion, the corresponding TG curve loses a lot of weight; comprehensive FTIR and TG-DSC analysis results show that Mg-Al-CMC is not a simple composite of CMC and LDHs, but forms an inorganic-organic supramolecular compound with an intercalation structure. And there is a strong interaction between the subject and the object.

4 is a high-resolution field emission scanning electron microscope (HRSEM) image of Mg-Al-LDH, Mg-Al-LDO and Mg-Al-CMC in Example 1. It can be seen from the figure that Mg-Al-LDH has leaf-loaded flaky hierarchical structure, and the flaky structure of Mg-Al-LDO obtained after calcination disappears, showing a granular/block shape; while Mg-Al-CMC returns to a uniform flaky structure.

The test method for the adsorption performance of materials to boron is as follows:

At room temperature, weigh 0.1g of Mg-Al-LDH, Mg-Al-LDO and Mg-Al ^- CMC respectively and add to 100mL 30 μg·mL sodium tetraborate simulated wastewater, place on a magnetic stirrer and stir at a speed of 300 r·min ^-1 , samples were taken at different time points of the reaction such as 20, 40, 60 min up to 8 h, centrifuged, and the supernatant was taken to measure its absorbance by amethymine hydrogen spectrophotometry, and the adsorption capacity q (mg g ^-1 ),

Formula 1)

In the formula: C ₀ is the concentration of inorganic boron in the wastewater before adsorption, μg·mL ^-1 ;

C is the concentration of inorganic boron in the wastewater during the adsorption process, μg·mL ^-1 ;

V is the total volume of the adsorption system (mL);

m ₀ is the added mass of adsorbent.

Fig. 5 is a graph showing the adsorption effect of boron by Mg-Al-LDH and Mg-Al-CMC in Example 1. It can be seen from the figure that the adsorption capacity of Mg-Al-CMC is significantly higher than that of Mg-Al-LDH, and the maximum adsorption capacity is nearly 9 mg·g ^-1 .

Example 2

(1) Synthesis of Mg-Al hydrotalcites with a molar ratio of 3: 7.68g magnesium nitrate and 3.75g aluminum nitrate were dissolved in

100mL distilled water to make a mixed solution; then dissolve 5.6g sodium hydroxide in 100mL distilled water to make a mixed alkali solution. The two solutions were dropped into a three-necked flask filled with 100 mL of distilled water under constant stirring at room temperature. After the dropwise addition, adjust the pH to 9-10 with 1mol·L ^-1 sodium hydroxide, and keep stirring at room temperature for 2h. The obtained mixture was suction-filtered and washed several times, and the obtained solid was dried in a constant temperature drying oven at 80°C for 4 hours to obtain Mg-Al-LDH2.

(2) Place the Mg-Al-LDH2 solid in a muffle furnace for calcination at 450°C for 4 hours to obtain a white solid Mg-Al-LDO2.

(3) Disperse the Mg-Al-LDO2 in 100mL distilled water with an ultrasonic cleaner to obtain a Mg-Al-LDO2 suspension. (4) Weigh 6.0g CMC and dissolve it in 100mL distilled water, add it dropwise to the Mg-Al-LDO2 suspension, and stir it mechanically

Stir for 4 hours to keep the solution in the flask alkaline at pH 9-10; transfer the mixture to a polytetrafluoroethylene hydrothermal reaction kettle at 100°C for crystallization in an oven for 12 hours, filter, wash, and dry at 80°C. Grinding to obtain a Mg-Al-CMC2 sample.

Fig. 6 is a comparison diagram of the boron adsorption effect of Mg-Al-CMC in Example 1 and Mg-Al-CMC in Example 2.

It can be seen from the above figure that the adsorption capacity of the two composite materials for boron is equivalent, and the adsorption capacity of Mg-Al-CMC2 for boron is slightly higher than that of Mg-Al-CMC, indicating that this material can be used as a special boron adsorbent to adsorb and separate wastewater Or boron in seawater.

The present invention is not limited to the above embodiments, and any technical solutions that are the same as or similar to those of the present invention fall within the protection scope of the present invention. The technologies, shapes and construction parts not described in detail in the present invention are all known technologies.

Claims (7)

1. A carboxymethyl cellulose ion intercalation hydrotalcite-like composite material: it is characterized in that the chemical general formula of the composite material is [M ²⁺ _1-x M ³⁺ _x (OH) ₂ ] ^x+ (A ^- ) _x mH ₂ O, where M ²⁺ is Zn ²⁺ , Ca ²⁺ or Mg ²⁺ , M ³⁺ is Fe ³⁺ or Al ³⁺ , and M ²⁺ and M ³⁺ are located on the main layer of hydrotalcite ; A ^2- is the interlayer carboxymethyl cellulose anion; x is the molar ratio of M ³⁺ /(M ²⁺ +M ³⁺ ), 0.1≤x≤0.33; m is the number of interlayer water molecules, m =3-6; the crystal structure of this material is that of a hydrotalcite-like material. 2. a kind of preparation method of carboxymethyl cellulose ion intercalation hydrotalcite composite material according to claim 1, its It is characterized in that it comprises the following steps: 1) Dissolve soluble divalent metal salts and trivalent metal salts in deionized water in a certain molar ratio, and stir to obtain solution A, in which the molar ratio of divalent and trivalent metal ions is (1~4): 1, divalent The metal ion concentration is 0.05~0.10 mol·L ^-1 ; 2) Under strong stirring, add sodium hydroxide solution drop by drop to solution A, adjust pH to 9~10 with sodium hydroxide solution, keep stirring at room temperature for 1~3h, filter and wash the resulting mixture several times to Neutral, the obtained filter cake is put into a constant temperature drying oven at 80~120℃ and dried for 4~6h to obtain a white solid B, which is the layered double metal hydroxide material LDH; 3) Put the solid B obtained above in a muffle furnace at 300-600°C for 3-5 hours to obtain a white solid powder C, which is a layered bimetallic composite oxide LDO; 4) Disperse the layered bimetallic composite oxide LDO prepared above in deionized water in a certain proportion to obtain LDO suspension D; 5) Sodium carboxymethyl cellulose solid was dissolved in distilled water to obtain sodium carboxymethyl cellulose solution E; 6) Mix the LDO suspension D obtained in the above step 4) with a certain proportion of sodium carboxymethyl cellulose solution E, and stir mechanically for 6~10 hours to keep the solution in the flask alkaline at pH 8~10; mix the above mixture Transfer to a polytetrafluoroethylene hydrothermal crystallization kettle, crystallize in an oven at 80~150°C for 12~20h, cool to room temperature, separate the solid and liquid from the product, wash to neutral and then vacuum dry at 60~85°C for 2~10h , that is, a hydrotalcite-like composite material intercalated with carboxymethyl cellulose, denoted as LDH-CMC. 3. preparation method according to claim 2 is characterized in that, described divalent metal divalent metal salt is the nitrate of Zn ²⁺ , Ca ²⁺ or Mg ²⁺ , and trivalent metal salt is Fe ³⁺ or Al ³⁺ nitrates. 4. The preparation method according to claim 2, characterized in that the concentration of the sodium hydroxide is 0.50-4.0 mol·L ^-1 , and the stirring speed of the vigorous stirring is 300-450 rpm. 5. preparation method according to claim 2, is characterized in that, the mol ratio of described sodium carboxymethyl cellulose and trivalent salt is 1:1～3:1. 6. preparation method according to claim 2, is characterized in that, the mass ratio of described layered bimetallic composite oxide LDO and deionized water is 1%～3%, and described sodium carboxymethyl cellulose The concentration of the solution E is 1%~3%, and the volume ratio of the LDO suspension D to the sodium carboxymethylcellulose solution E is 1:1~1:3. 7. An application of the carboxymethyl cellulose ion intercalation hydrotalcite-like composite material according to claim 1 in the adsorption and separation of boron in water bodies.